It is known to produce white aluminum hydroxide, for instance with a minimum 93% brightness (based upon a 100% TiO.sub.2 reference standard), by a sinter process wherein wet red mud or bauxite is mixed with lime and soda to form a thick slurry. The slurry is sintered to form a soda-lime sinter product composed of insoluble silicate and a soluble aluminate.
U.S. Pat. No. 3,796,789 is an example of such procedure. The soda-lime sinter product, in which most of the color imparting organic compounds have been removed by the sinter process, is leached, and the leachate subjected to a digestion process. The liquor coming from the digestion is then treated with slaked lime for lowering iron.